1. Technical Field
The present disclosure relates to a signal processor and a method for compensating loudspeaker aging phenomena.
2. Description of the Related Art
Audio equalization involves performing compensating processes on an audio signal in order to differently affect the amplitude of the signal at various frequency bands. The result is an alteration of the frequency response of a device. Amplitude is generally measured in decibels (dBs) and modifying the amplitude of the signal at different audio bands can greatly affect both a user's audio experience as well as the perceived quality of the signal.
Recently audio equalization has become quite useful and important to overcome the poor frequency response and non-linearity of actual loudspeakers. This happens in a growing number of segments which goes from the TV to the notebook/netbook markets as well as in the mobile, smart-phone, personal multimedia player (PMPs) appliances or in the more recent all-in-one or tablet PCs segment.
Loudspeaker performances, indeed, are strictly related to their mechanical sizes, to the adopted materials and to the surrounding enclosure. The frequency response, in particular, is greatly affected by those elements. For instance, a good response to the lower frequencies can only be achieved with wide speaker sizes and huge resonance chambers. Achieving an overall flat response throughout the typical audio spectrum (e.g., 20 Hz . . . 20 KHz) is quite difficult and only professional equipment, nowadays, is offering such performances.
The continuous trend to reduce the size of portable and hand-held devices, for instance, along with the efforts aiming to reduce the cost of the overall device force manufactures to sacrifice the resulting audio response. Even worst, this happens in times when the capability to play audio contents is becoming a common feature and, therefore, the expected audio performances of such devices are becoming more and more important.
A further evolution negatively affecting audio quality is driven by the more recent LED technology used for the backlight of the screen in place of the widely adopted cold-cathode fluorescent lamp (CCFL). As a result new ultra-thin TV screens are now available off-the-shelf. This all has greatly affected the loudspeaker quality, preventing good audio performances and, therefore, has turned equalization and speaker compensation technologies into a major mean to recover adequate frequency responses. TV manufactures are investing efforts and resources in developing and tuning equalization devices or even more advanced audio enhancements algorithm in order to recover good audio performances. Audio quality has become a major differentiation factor, one of the top most important attributes, and is influencing consumer's television buying decision.
Nowadays various tools and graphical user interfaces greatly helps users to program the equalization parameters but still finding the best tuning is a quite challenging task. Notably such kind of tools are assuming a flat (e.g., 0 dB) frequency response when no equalization filters are applied, irrespective of the actual speaker frequency response.
Even if the equalization parameters are computed and tuned in order to compensate the loudspeaker frequency response, which is far from being flat over frequency, the result is still a static set of parameters. How such equalization parameters will actually perform on different speaker sets is not easy to be predicted due to the variations of the transducer characteristics. Moreover electro-mechanic parameters could change over time modifying the loudspeaker frequency response and the applied static equalization would be quite ineffective to compensate for such variations.
According to the known art, in WO 97/03536 is described a loudspeaker circuit for monitoring both the pressure and the displacement at the speaker diaphragm with a view to developing a related feedback signal. The coupling between the loudspeaker and its environment can be modified by means of filtering the input signal and source acoustic impedance of the speaker.